This invention relates to a process for the production of spray-dried granular alkaline detergent compositions containing, as a surfactant system, an ethoxylated nonionic surfactant and a zwitterionic surfactant, wherein the degradation of the zwitterionic detergent during the crutching and spray-drying of the composition is minimized.
In the preparation of spray-dried detergent granules, an aqueous mixture of the various components of the granules (the crutcher mix) is sprayed or otherwise introduced into what is essentially a drying tower. As the droplets of the crutcher mix proceed through the drying tower, the water is flashed off and solid or semiporous detergent granules are formed. The advantages of spray-dried detergent granules over granules obtained by simple dry-mixing of the individual ingredients include improved homogeneity and more even dissolving rates for the individual components having the same particle size. That is to say, each granule contains the various ingredients of the composition in the same ratios and proportions introduced into the original crutcher mix. This provides obvious advantages over simple dry-mixed detergent formulations, inasmuch as dry-mixing can result in a lack of homogeneity in the final detergent formulation such that the user is never certain of the composition of any given portion of such products.
It is taught in the art that the incorporation of various zwitterionic surface-active agents, particularly in combination with certain nonionic surface-active agents, in detergent compositions yields detergency benefits. Thus, in U.S. Pat. No. 3,351,557, Almstead et al, issued Nov. 7, 1967, it is taught that built liquid detergent compositions comprising certain nonionic surfactants, zwitterionic sultaine surfactants, a detergency builder salt, a polymeric emulsion stabilizer and water, would provide superior detergency characteristics under a wide variety of conditions, and particularly in cool water washing. Additional detergent compositions including zwitterionic sultaine components are described in British Pat. No. 1,331,062, Pearson et al, issued Sept. 19, 1973 and Belgian Specification 814,987, published Nov. 14, 1974. U.S. Pat. No. 3,929,678, Laughlin et al, issued Dec. 30, 1975, discloses that detergent compositions incorporating specifically defined ethoxylated zwitterionic surfactants, together with cosurfactants, provide exceptionally good clay soil removal characteristics which are relatively insensitive to water hardness level and temperature changes. Additional detergent compositions comprising this type of ethoxylated zwitterionic surfactant are disclosed in U.S. Pat. No. 3,925,262, Laughlin et al, issued Dec. 9, 1975 and U.S. Patent Application Ser. No. 603,837, Laughlin et al, filed Aug. 11, 1975.
The crutching and spray-drying process, while possessing the advantages which are described above, does create a problem with regard to the incorporation into granules of relatively alkalinity-sensitive ingredients, of which zwitterionic surfactants are an example. Although it would clearly be very desirable to add zwitterionic surfactants directly to an alkaline crutcher mix prior to spray-drying, it has been found that such addition results in the loss of the zwitterionic surfactants through degradation into various compounds, such as amines.
The zwitterionic surfactants could, of course, be incorporated into the compositions after spray-drying, for example, by dry-mixing or spraying on, but the necessity of such an extra step in the process is undesirable. In addition, the use of such methods makes it difficult to distribute the component uniformly throughout the granular composition.
It is therefore the object of this invention to provide an improved process for the incorporation of zwitterionic and nonionic surfactants into spray-dried granular detergent compositions.
It is a further object of this invention to provide a process whereby zwitterionic surfactants may be incorporated into an aqueous alkaline crutcher mix and subsequently spray-dried, with minimal loss of the surfactants through degradation.